Design and synthesis of amorphous SiO_x structures generated by Sn quantum dots: growth mechanism and luminescent origin

SiO_x structures with different diameters of a few hundreds of nanometers and/or a few micrometers are prepared using applied thermal evaporation. Subsequently, Sn quantum dot-based SiO_x architectures are synthesized via the continuous steps of the carbothermal reduction of SnO₂, substitution of Sn⁴⁺ for In³⁺, thermal oxidation of Si, Sn sublimation, interfacial reaction, and diffusion reaction consistent with corresponding phase equilibriums. Several crystalline and spherical-shaped Sn quantum dots with diameters between 2 and 7 nm are observed in the amorphous SiO_x structures. The morphological evolution, including hollow Sn (or SnO_x) sphere and wire-like, worm-like, tube-like, and flower-like SiO_x, occurs stepwise on the Si substrate upon increasing the given process energies. The optical characteristics based on confocal measurements reveal the as-synthesized SiO_x structures, irrespective of whether crystallinity is formed, which all have visible-range emissions originating from the numerous different-sized and -shaped Sn quantum dots permeating into the SiO_x matrix. In addition, photoluminescence emissions ranging between ultraviolet and red regions are in agreement with confocal measurements. The origins of the morphology- and luminescence-controlled amorphous SiO_x with Sn quantum dots are also discussed. (paper)